1. Field of the Invention
The present invention relates to ultrasound imaging, and more particularly to techniques for ultrasound imaging of internal organs and vascular structures via the gastrointestinal wall.
2. Description of the Related Art
In recent years ultrasound imaging techniques have significantly developed, particularly where images of internal structures lying deep within the patient are desired through the use of non-invasive, non-surgical procedures. Cardiac imaging of organs near the esophagus is achieved using an ultrasonic transducer attached to a probe which is inserted into the mouth of a patient and placed against the interior wall of the esophagus near the internal organ or structure of interest. Cardiac imaging has often been achieved through the use of transesophageal ecocardiography (TEE). The proximity of the esophageal transducer to the image structures allows the use of resolution enhancing higher frequency transducers. However, adequate visualization of the abdominal aorta, its branches and other organs and structures in the abdominal area is not possible through the use of TEE. The TEE transducer falls away from the posterior wall of the stomach once it leaves the esophagus and enters the gastric cardia, where interposed air prevents imaging of the abdominal vascular structures.
It is often desirable to obtain high resolution imaging of the internal structures and organs in the abdominal area through the use of non-invasive, non-surgical procedures. One such application is monitoring of blood flow to the kidney through ultrasonic imaging. Loss of blood flow to the kidney is a common cause of kidney failure requiring patient dependency on hemodialysis. No known technique presently exists to reliably monitor blood flow to the kidney through minimally-invasive means. If such low blood flow is detected, intervention may be possible to prevent kidney failure. Another application is imaging of the vena cava which may be useful when filters are implanted in the vena cava to trap blood clots. Under present techniques, implantation of filters in the vena cava requires the use of dyes and x-rays.
Invasive surgery is generally required to obtain sufficiently detailed and clear images of internal organs and structures near the stomach. Three-dimensional CT scanning and magnetic resonance angiography have the potential to fulfill this imaging need, but these technologies have yet to be fully developed. Transabdominal duplex scanning is yet another procedure for evaluating the abdominal organs and structures of the patient, particularly the abdominal aorta and its major branch vessels for the presence of significant atherosclerotic disease. However, major limitations prevent a more widespread application of this technique. For example, for length of time required to perform a complete vascular duplex examination of the abdominal aorta, celiac access, superior mesenteric, and both renal arteries can exceed one hour, even when the examination is performed by experienced vascular technologists. In addition, this technique requires the use of lower frequency transducers (less than 5 MHZ) to traverse this distance. The depth of structures to be imaged and the use of low frequency transducers may result in poor resolution and image quality. Intestinal gas and abdominal wall fat may also limit the resolution and amount of information obtained during transabdominal vascular ultrasound imaging.
U.S. Pat. No. 5,394,878 entitled "Method for Two Dimensional Real Time Color Doppler Ultrasound Imaging Of Bodily Structures Through The Gastro Intestinal Wall", issued on Mar. 7, 1995, discloses a method for two dimensional real time color Doppler ultrasound imaging of bodily structures through the gastrointestinal wall. This patent discloses imaging of deep internal organs and vascular structures by introduction of a transducer on the end of a probe into either the colon or the esophagus of a patient. The transducer can then be positioned adjacent to the organ or vessel of interest for ultrasonic imaging. U.S. Pat. No. 5,492,126 entitled "Probe For Medical Imaging And Therapy Using Ultrasound", issued Feb. 20, 1996, also discloses a probe for inspecting an internal organ of a patient. The patent discloses a probe having a flexible portion at a distal end of the probe.
However, these inventions are unable to obtain the level of ultrasonic imaging resolution required to adequately diagnose or observe conditions of the internal structures or organs of interest. While these probes can be guided into either the colon or the esophagus of the patient, they cannot be positioned to desired locations near the wall of the stomach to adequately obtain clear and detailed ultrasound images of certain organs or vessels. Particularly, bending of the probe along the entire length of the body prevents the transducer from avoiding intervening gases which is necessary to obtain high resolution images. Imaging of abdominal organs and structures, for example the abdominal aorta, kidneys, superior mesenteric, both renal arteries and the vena cava, is limiting under known techniques. Imaging of blood flow within blood vessels in the abdominal region is also limiting under known techniques.
A flexure control mechanism such as those found in endoscopes may be used to control the bending of the probe near the ultrasonic transducer. Such a concept has been disclosed in U.S. Pat. No. 5,492,126 entitled "Probe For Medical Imaging and Therapy Using Ultrasound", issued in Feb. 20, 1996. However, such flexure control is still unable to obtain the level of precise positioning required to adequately image certain internal organs and structures.